Photo: DTU Aqua

Parasites hinder organic trout production

Monday 27 May 19


Alfred Jokumsen
Senior Adviser
DTU Aqua
+45 35 88 32 57

Project ShelterFish website

Project ShelterFish is a collaboration between DTU Aqua, the Department of Veterinary and Animal Sciences at the University of Copenhagen, Dansk Akvakultur, Lihme Dambrug (fish farm), Vork Dambrug (fish farm), and Ravnstrup Mølle.

See the project website 
Optimum water conditions, hiding places for fish, and the prevention and reduction of parasites and bacteria to secure organic trout fry.

Less illness, reduced medicine consumption, and the mortality rate in organic trout production—these are the goals of the new research project ShelterFish, spearheaded by DTU Aqua. The overall idea is that less stress leads to healthier fish and fewer diseases.

The project seeks to address two diseases in particular that stand in the way of organic trout production in Denmark: One is a bacterial infection that causes ulcers in the adult fish. The other is a parasitic infection that affects the smallest fish—the fry—and causes a high mortality rate.

“Parasites in trout fry pose a big problem. It creates a bottleneck, as the high mortality rate makes it difficult for organic trout farms to get sufficient fry,” says Senior Adviser Alfred Jokumsen from DTU Aqua. He is the Project Manager of ShelterFish, which is part of the Organic RDD 4 program coordinated by ICROFS (International Centre for Research in Organic Food Systems) and funded by The Ministry of Environment and Food of Denmark.

Organic fish can only be treated for parasites twice a year

If a fish is to be sold as organic, it must have been treated with parasite medicine no more than twice a year. Since 1 January 2016, organic fish needs to be organic throughout their lives, from the moment the eggs are fertilized to 14-36 months later, when the fish have reached the relevant market sizes and are sent to the supermarkets.

“If the fish are given a third parasite treatment within 12 months, the fish farmer can no longer sell them as organic. They can still be sold as conventional fish, but at a significantly lower price. And by then, the fish farmer has already had a lot of expenses for producing the fish according the rules of organic farming,” says Alfred Jokumsen.

The other disease tackled by the project is a bacterial infection known as red mark syndrome (RMS). The disease does not have a particularly high mortality rate, but is very contagious. The fish develop ulcers, and since they often get them as adults, this can mean that up to 30 per cent are discarded in the slaughtering process. Consequently, red mark syndrome is a key issue in the ShelterFish project, and they will perform tests to see if the fish can be immunized to the bacterium if they encounter it earlier in life.

More shade and less organic matter

The goal of the ShelterFish project is to find solutions and improve the living conditions of the fish, thus making them more resistant to the two diseases. The project will work to create a better water environment and better living conditions, including through the development of a kind of shade or hiding places for the fish to hide in, like they would in the wild, and an examination of whether this will make them less stressed.

The quality of the water plays a key role in terms of both parasites and red mark syndrome. Previously, the water was tested for chemicals and nutrients when assessing the water quality of fish farms. However, it is also important to look at the amount of organic matter in the water.

“Organic substances from feed or faecal matter make fantastic bacterial culture media. So the more organic matter there is, the more bacteria there will be in the water, and thus the risk of disease outbreaks among the fish will also be greater,” says Alfred Jokumsen.

Therefore, methods for reducing the amount of organic matter in organic fish farms, thereby reducing the amount of bacteria, are being investigated.

Potential big difference for Danish aquaculture industry
Organic trout production is only a small part of Danish food production, but organic foods are increasingly popular. An earlier research project, RobustFish, showed that consumers were willing to pay extra for organic fish, and that the price difference is also expected to be the same, even when the supply of organic fish will increase. The survey also showed that one of the reasons why 80 per cent of consumers never bought organic fish was a lack of availability.

“The market for organic foods is growing rapidly. This also applies to organic fish and shellfish. Organic fish farming is therefore estimated to have great potential, and Dansk Akvakultur wants to increase the production of organic fish in both onshore and offshore fish farming,” says Veterinarian Niels Henrik Henriksen from Dansk Akvakultur (an industry organization for Danish fish and shellfish farmers).

“In order for the farmers to make the switch to organic farming, it’s important for them to know that the production of fry is stable,” says Alfred Jokumsen.

Like the many other aquaculture research projects at DTU Aqua, ShelterFish is the result of a close dialogue with the industry—and in this case a concrete case of needing to find solutions to problems with parasites and red mark syndrome.

“Organic trout production is currently very challenged by the problems related to the lack of treatment options for common parasitic diseases in the fry, while the bacterial skin disease leads to financial losses due to discarding in the slaughter and export process. We see great potential in the ShelterFish project and are very optimistic about the project resulting in useful solutions that can help the organic trout farmers soon,” says Niels Henrik Henriksen.

Improved animal welfare results in improved economy

Project ShelterFish launched on 1 January and will run for three years. Alfred Jokumsen and the other researchers behind the project expect that the work will increase the availability of organic trout fry and reduce the loss of fish discarded at slaughter due to red marks and thus pave the way for bigger and more profitable production of sales-ready organic trout. If they succeed, it will also affect conventional production.

“Obviously, the fewer sick fish, the fewer dead fish, and the better ethics and animal welfare—which is what it’s ultimately all about—the better the output will be, and thus the farmer’s economy will also improve,” says Alfred Jokumsen.

The project is a collaboration between DTU Aqua, the Department of Veterinary and Animal Sciences at the University of Copenhagen, Dansk Akvakultur, Lihme Dambrug (fish farm), Vork Dambrug (fish farm), and Ravnstrup Mølle.

Facts about organic trout production

  • The fish must be produced according to the rules of organic farming right from the fertilization

  • No more than two medicine treatments for parasites and bacteria a year

  • Use of low-impact additives

  • No more than 25 kilos of fish per m3 of water for onshore fish farms and 10 kilos of fish per m3 for offshore fish farms

  • No GMOs or artificial colouring in the feed

  • At least 60 per cent oxygen saturation in the water

  • Environmental approval and requirements for daily monitoring of important environmental and health parameters

  • Organic fish farming is not allowed to take place in closed recirculation systems, with the exception of hatching/fry farming